1. Field of the Invention
The present invention relates to determining the running speed of an integrated circuit. More specifically, the present invention relates to an integrated circuit with an internal clocking system where the clock period represents the speed of the clocked circuit.
2. Discussion of Background Information
Integrated circuits made according to the same manufacturing process are typically not created equal. Due to various imperfections in the manufacturing process from one lot of chips to the next, and even with the same lots, individual chips may have different running speeds. The computing market has been able to take advantage of this manufacturing flaw by charging more for faster chips and less for slower chips. This market segmentation requires sorting the chips into different speed classifications.
It is common to identify timing bins with two or more clock speed reference points for the ICs operation. For example, a fast bin for chips which operate faster than expected, a nominal bin for chips that operate at the expected speed, and a slow bin for chips that operate slower than expected. A practical example is the Pentium 4 processor chip, whereby the same manufactured circuit is binned at steps of 200 MHz, e.g., 2.8 GHz goes into the fast bin and will be the most expensive chips with the lowest timing yield, 2.6 GHz goes into the nominal bin and will be cheaper than the 2.8 GHz chip, and 2.4 GHz chips will go to the slow bin and be the cheapest of the three. Another example the Intel Centrino processor with speed bins at 1.1 GHz, 1.2 GHz and 1.5 GHz.
Currently manufactured IC's do not have the ability to communicate their running speed. Empirical methods are used in that the same IC is tested repeatedly at different speeds to determine if the chip works reliably or not at that speed. Thus for example, an IC which operates reliably and consistently when tested at 2.4 GHz but erratically or not at all at 2.6 GHz indicates that the chips' actual speed is somewhere between 2.4 and 2.6 GHz. The chip could be accepted as a 2.4 GHz chip, or tested to further narrow its operating range (e.g., whether the chip works reliably between 2.4 and 2.5 GHz). Ultimately the chip is labeled at a speed of the lower of the selected range, as opposed to its actual running speed. It is therefore not uncommon for chips to be able to operate faster than their advertised running speed. It is also not uncommon for users to modify their system to “overclock” their PC to access the additional speed potential.